Field of the Invention
The invention relates, in general, to press-forming objects and, in particular, to a new and useful coated-core press for producing coated tablets and to a method and apparatus for transferring cores into a bottom layer of powder material.
A coated-core press is known from U.K. patent No. 858,538. It has considerable disadvantages with respect to the transfer action of the cores from a core storing tube over an annular disc into one of the dies of the die tables. The cores fall out from the core storing tube on the annular discs of the transfer mechanism and are received by fork-type receiving elements transferring the cores into receiving apertures of the transfer heads. Therein are guided punches having short extensions, such punches are supported by means of upper annular cams so as to be raised or lowered in the transfer heads. The punches press with their lower extensions of the cores being guided on the annular disc by means of the transfer mechanism, until the transfer heads are brought into register with the dies of the die table. The cores will then fall under the action of the punches into the dies. Prior to that, the lower punch guided in the die is lowered, and the die is filled up with the bottom layer of powder material serving for coating. Then, the lower punch is further lowered by a small amount. Only then is the core placed onto the bottom layer present in the die, the lower punch being, then, further lowered and the die being filled up with the top layer of powder material. Finally, coating of the core is finished between lower and upper punches by means of the upper punch entering into the die.
For accurate positioning of the core in the bottom layer of powder material, there is available a very short period of time only with the known coated-core press, namely the limited period of time during which the transfer head of the transfer mechanism and the associated die are guided accurately concentrically with respect to each other. This period of time may, in case of low quantities of approximately 20,000 tablets per hour, i.e. low rotational speed of transfer mechanism and die table, be just sufficient to bring the core under the action of its own weight centrally into the bottom layer of powder material inside the die. For higher quantities of up to 100,000 per hour and, thus higher rotational speeds of transfer mechanism and die table, this short period of time of register of the partial circles of die and transfer head will, however, not be long enough to bring the core safely centrally into the bottom layer of powder material inside the die.
Furthermore, the centrifugal force acting on the core, such force increasing by a square law with respect to the rotational speed, causes another disadvantage in that the core, possibly just brought centrally into the die, will slip outwardly on the bottom layer of powder material, so that exact centering of the core inside the coated-core tablet is not possible.
For the known coated-core press, it is, thus, disadvantageous both because the cores are subjected to friction on the annular disc which is a stationary component comprising segment-type cuts to receive two die tables, and also because the cores fall substantially under the action of their own weight from the transfer heads into the dies, thus a relatively slow speed of the coated-core press is effected.
Accordingly, it is an object of the invention to provide an improved device for positioning a core material inside of the powdered material in the formation of a table and which includes a transferring mechanism for holding the core and which transfer mechanism has a core punch with a vacuum system or other gripping means for engaging a core and positioning it in a dye which contains the powdered material.
A further object of the invention is to provide a method of positioning a core in a powdered material in the formation of a tablet which comprises employing a punch having a gripping mechanism for engaging the core material and transferring it into a die containing the powdered material and for moving the punch to accurately position in the core in respect to the powdered material during the formation of the tablet.
A further object of the invention is to provide a device for positioning the core in a tablet in which the core is surrounded by a powdered material which is simple in design, rugged in construction and economical to manufacture.